I am still having this bug. Upon significant back and forth, we have not been able to reproduce it on Tim's setup (thanks Tim!), but it's very firmly repeatable on mine. I'd love to see if someone else could give it a shot.

Note that the full secnario to get it to fail is for a specific socket (in this run above, it's Socket 0) goes from UDP transaction to TCP transaction and then you try and use it for UDP again. In that scenario it won't work (for me)...